The document provides a comprehensive overview of Python functions, including their definition, purpose, and types like built-in and user-defined functions. It also covers concepts such as variable scope and lifetime, recursion with its advantages and disadvantages, and the use of lambda functions. Additionally, it explains Python modules and packages, detailing how to import them and the structure required for organizing related files.

1. Python Functions

2. What is a function in Python?
• Is a group of related statements that perform
a specific task
• Help break our program into smaller and
modular chunks
• As program grows larger and larger, functions
make it more organized and manageable
• Furthermore, it avoids repetition and makes
code reusable

3. Syntax of Function

4. Example of a function

5. Docstring

6. The return statement

7. How Function works in Python?

8. Scope and Lifetime of variables
• Scope of a variable is the portion of a program where
the variable is recognized
• Parameters and variables defined inside a function is
not visible from outside. Hence, they have a local
scope.
• Lifetime of a variable is the period throughout which
the variable exits in the memory.
• The lifetime of variables inside a function is as long as
the function executes.
• They are destroyed once we return from the function.
Hence, a function does not remember the value of a
variable from its previous calls.

9. Example

10. Types of Functions
• Can be divided into the following two types:
– Built-in functions: Functions that are built into
Python
– User-defined functions: Functions defined by the
users themselves

11. Arguments

12. Python Default Arguments

13. Python Keyword Arguments

14. Python Arbitrary Arguments

15. Python Recursion
• What is recursion in Python?
• Python Recursive Function
• Advantages of Recursion
• Disadvantages of Recursion

16. What is recursion in Python?
• Recursion is the process of defining something
in terms of itself
• A physical world example would be to place
two parallel mirrors facing each other
• Any object in between them would be
reflected recursively

17. Python Recursive Function

19. Advantages of Recursion
• Make the code look clean and elegant
• A complex task can be broken down into
simpler sub-problems using recursion

20. Disadvantages of Recursion
• Sometimes the logic behind recursion is hard
to follow through
• Recursive calls are expensive (inefficient) as
they take up a lot of memory and time
• Recursive functions are hard to debug

21. Python Anonymous/Lambda Function
• What are lambda functions in Python?
• How to use lambda Functions in Python?
– Syntax of Lambda Function in python
– Example of Lambda Function in python
– Use of Lambda Function in python

22. What are lambda functions in Python?
• In Python, anonymous function is a function
that is defined without a name.
• While normal functions are defined using the
def keyword, in Python anonymous functions
are defined using the lambda keyword.
• Hence, anonymous functions are also called
lambda functions.

23. How to use lambda Functions in
Python?
• Syntax of Lambda Function in python

24. Example of Lambda Function in python

25. Use of Lambda Function in python

27. Python Global, Local and Nonlocal
variables
• Global Variables in Python
• Local Variables in Python
• Global and Local Variables Together
• Nonlocal Variables in Python

28. Global Variables in Python

30. Local Variables in Python

31. Global and Local Variables Together

33. Nonlocal Variables in Python

34. Python Global Keyword
• Python global Keyword
– Rules of global Keyword
– Use of global Keyword (With Example)
• Global Variables Across Python Modules
• Global in Nested Functions in Python

35. Python global Keyword
• The basic rules for global keyword in Python are:
– When we create a variable inside a function, it’s local
by default
– When we define a variable outside of a function, it’s
global by default. We don’t have to use global
keyword.
– We use global keyword to read and write a global
variable inside a function.
– Use of global keyword outside a function has no effect

39. Global Variables Across Python
Modules

41. Global in Nested Functions

42. Python Modules
• What are modules in Python?
• How to import modules in Python?
– Python import statement
– Import with renaming
– Python from...import statement
– Import all names
• Python Module Search Path
• Reloading a module
• The dir() built-in function

43. What are modules in Python?
• File containing Python statements and
definitions
– Example: example.py, is called a module
• Use to break down large programs into small
manageable and organized files.
• Provide reusability of code
• Can define our most used functions in a
module and import it, instead of copying their
definitions into different programs

44. How to import modules in Python?
• Python import statement
• Import with renaming
• Python from...import statement
• Import all names

45. Python import statement

46. Import with renaming

47. Python from...import statement

48. Import all names

49. Python Module Search Path
• While importing a module, Python looks at
several places.
• Interpreter first looks for a built-in module then
(if not found) into a list of directories defined in
sys.path.
• The search is in this order.
– The current directory.
– PYTHONPATH (an environment variable with a list of
directory).
– The installation-dependent default directory.

51. Reloading a module

52. The dir() built-in function
• We can use the dir() function to find out
names that are defined inside a module.

54. Python Package
• What are packages?
• Importing module from a package

55. What are packages?
• We don't usually store all of our files in our
computer in the same location.
• Similar files are kept in the same directory, for
example, we may keep all the songs in the
"music" directory.
• Analogous to this, Python has packages for
directories and modules for files.

56. • As our application program grows larger in size
with a lot of modules, we place similar modules
in one package and different modules in different
packages.
• Similar, as a directory can contain sub-directories
and files, a Python package can have sub-
packages and modules.
• A directory must contain a file named __init__.py
in order for Python to consider it as a package.
• This file can be left empty but we generally place
the initialization code for that package in this file

58. Importing module from a package
• We can import modules from packages using the
dot (.) operator.
• For example, if we want to import the start
module in the above example, it is done as
follows.
– import Game.Level.start
• Now if this module contains a function named
select_difficulty(), we must use the full name to
reference it.
– Game.Level.start.select_difficulty(2)

59. • We can also import the module without the
package prefix as follows
– from Game.Level import start
• We can now call the function simply as
follows.
– start.select_difficulty(2)

60. • Yet another way of importing just the required
function (or class or variable) form a module
within a package would be as follows.
– from Game.Level.start import
select_difficulty
• Now we can directly call this function.
– select_difficulty(2)

61. Thank You !